Researchers Working to Establish an Odor Index

It's little wonder that scientists are obsessed with numbers, since so much of their work relies on measuring and quantifying. They've got a number for just about everything.

Light is measured in candelas. Sound in decibels. If you're running a pneumatic drill, chances are you're generating 80 decibels of ear-piercing noise.

But ask a scientist how bad the pig farm down the road smells, and you'll probably get a quizzical look and a vague answer. When it comes down to odor, the nose knows when something stinks, but there's no olfactory equivalent to decibels.

So along comes Seth Hapner, who is finishing up his master's degree in environmental engineering at Penn State, with a possible solution to this dilemma. Hapner, along with Bradley A. Striebig, who heads the environmental technology group at Penn State's Applied Research Laboratory, has developed what he calls an "odor index."

Current Meters Too Subjective

He used off-the-shelf technology to create an instrument-based system that can detect gases given off by any substance and in what quantities, and then put a number on it. If the odor index value is 1,000, you should be able to detect it. If the index is 10,000, and the chemical is hydrogen sulfide, you should just be able to detect the fine scent of rotten eggs. And if it's 100,000, you'll want to plug your nose and get the heck out of there.

The most commonly used system today involves submitting air samples to various labs around the country that have "odor panels." If an environmental engineer wants to know how bad something smells, he or she can submit a sample, and the folks who serve on the odor panel will take a sniff and render up their judgment. (And you thought you had it bad.)

The problem with that system, Hapner says, is it's very subjective, despite efforts by the labs to get reliable people to serve on the panels.

"We're trying to come up with a method that would be repeatable in any lab around the country," Hapner says.

Tinkering to Keep Stink Down

If a particular odor could be systematically quantified, he says, it could help folks who are in charge of such things as disposing of sewage wastes. They could determine more precisely when they can use the waste as fertilizer without whipping up a storm of protests from downwind residents, for example. Environmental agencies in Pennsylvania and New Jersey, along with the federal Environmental Protection Agency, are sponsoring Hapner's research, and they have already tried it out successfully in the field.

Sewage treated in a major Pennsylvania plant, for example, had a 99 percent reduction in odors because of treatment procedures, Hepner says. If the final product had still stunk, he adds, the system would have told officials exactly where along the treatment stream the procedures had failed.

Here, very briefly, is how the index works: Hapner collects solid samples, like clumps of dried sewage, and takes them back to the lab in sealed plastic containers. Overnight, the clumps give off gases containing chemicals. Those gases are analyzed by a gas chromatograph, which tells which gases are present, and in what quantities.